The city is being hit with a $50 million lawsuit by the family of a 13-year-old Queens boy who was chased, tackled and allegedly assaulted by cops last summer at a Far Rockaway burger joint.

James Reed, 13, was bashed in the head with a flashlight, and a heavy-set cop pressed his knees into the small of his back – before the attackers identified themselves as cops, the boy’s lawyer, Seth Greenberg, said yesterday.

Greenberg said the July 15 surveillance video from the White Castle on Beach Channel Drive proves the case.

Greenberg said he doesn’t yet know the names of the cops. But an NYPD spokesman, Lt. Stephen Biegel, confirmed that an incident occurred – and was probed by the Queens DA, who found no grounds for criminal action.

“We do have an open internal-affairs investigation on this case,” Biegel said. “So we’re not going to get into the details of this.”